Install linked package dependencies, closes #673.

Also add a "unlink" alias to "uninstall".
Some fixes.
Merge branch 'master' of github.com:bower/bower into link-install-deps
Merge branch 'master' into link-install-deps
Merge branch 'master' of github.com:bower/bower into link-install-deps
Merge pull request #891 from bower/link-install-deps

Install linked package dependencies, closes #673.